1. Field of the Invention
This invention relates to an apparatus and method for heating, thawing and/or demoisturizing materials and/or objects, and more particularly to such an apparatus and method employing microwave techniques to perform the requisite function.
2. Description of the Prior Art and Related Patent Applications
It is often required in any one of a number of industries to heat, thaw, or demoisturize materials, especially particulate type materials. Sometimes, it is even necessary to perform these functions on objects which are embedded in the material or otherwise located therein. A typical example is found in mining or other industries where natural and man-made particulate materials, such as lime, coke, coal, sand, gravel and ores (iron, etc.) are collected and transported, typically in broken or granular form, by open rail cars or the like. Typically, the open rail cars collect moisture due to rain, high relative humidity or from other sources. In cold or freezing weather these materials often become frozen, which renders discharge of the material stored in the rail cars difficult or impossible.
Various thawing methods and apparata have been proposed in the Prior Art. Early thawing efforts described in U.S. Pat. No. 2,507,775 included the building of wood fires under the cars, the holding of gas jets against the sides of the cars in various places, and the use of steam baths to which parts of the car or the whole care were subjected. These methods, have, however, proven unacceptable since they either subject the rail car to excessive localized temperatures which can cause buckling or other serious structural weakening of the car, descruction of the paint on the car, and/or in part insufficient heat to the car and its contents to ensure thorough thawing and/or demoisturizing of the material contained therein.
Modern attempts at providing economic and efficient railway car thawing systems have utilized electrical energy heating devices to perform the thawing. Thus, as is disclosed in U.S. Pat. No. 3,569,657, microwave energy is emitted through an access opening provided in the bed of a transport vehicle such as a truck trailer or a railway vehicle car, with the transport vehicle then serving as a microwave cavity for heating the contents thereof. However, this microwave heating system would appear to find utility only with special purpose vehicles specifically provided with microwave access openings, with the vehicles being closed to provide the requisite microwave cavity. Thus, in order to implement this system on a large scale, a massive capital expenditure would be required of the railroad industry to refurbish existing rail coal cars and the like. Furthermore, the microwave energy emitted through the access opening is progressively absorbed such that little microwave energy reaches the truck contents remote from the access opening, resulting in uneven thawing. While this problem can be remedied by employing microwave sources with higher power output, there are limited sources for such high power devices, which in any event are typically less reliable and entail more maintenance. Additionally, considerable leakage of the microwave energy occurs via the access opening, presenting a potential health hazard, and reducing the operating efficiency.